Corrosion inhibition

ABSTRACT

Use of mono-, di-, and triphosphoric acid esters of triethanol amine and mixtures thereof to inhibit the corrosion of metals by oxygen-bearing waters.

United States Patent 1 [111 3,868,217 Hollingshad Feb. 25, 1975 CORROSION INHIBITION [56] References Cited [75] Inventor: William Robert Hollingshad, Bethe] UNITED STATES PATENTS Park, Pa. 2,737,498 3/1956 Frasch 252/389 [73] Assignee: Calgon Corporation, Robinson Townshi Pa.

3,422,166 1/1969 22 i May 9 1974 3,787,319 1/1974 Larsen 21/27 A [21] Appl 468347 Primary Examiner-Barry S. Richman Related US, A li ti D t Assistant Examiner-Da1e Loverchleck [63] Continuation-impart of Ser. No. 347,009, April 2, Attorney Agent or Flrm Mamn Katz; Harry 1973, abandoned. Wesflake [52] 11.8. C1. 2l/2.7 A, 21/27 R, 252/389 A, [57] ABSTRACT 252/392! 252/394 Use of mono-, di-, and triphosphoric acid esters of tri- [5 1] Int. Cl. C23f 11/14, C23f 11/16 ethanol amine and mixtures thereof to inhibit the Cop [58] Field of Search 21/27 A, 2.5 A; 252/148, rosion of metals by oxygembearing waters 4 Claims, No Drawings CORROSION INHIBITION This application is a continuation-in-part of U.S. Ser. No. 347,009, filed Apr. 2, 1973 and now abandoned.

This invention relates to the use of the mono-, di-, and triphosphoric acid esters of triethanol amine N(CH CH O(PO where n=l-3 and mixtures thereof, alone or in combination with certain triazoles. thiazoles and mixtures thereof, for inhibiting corrosion of metals by oxygen-bearing waters.

Oxygen corrosion is, of course, a serious problem in any metal-containing water system. The corrosion of iron and steel is of principal concern because of their extensive use in many types of industrial and municipal water systems. Copper and its alloys, aluminum and its alloys, and galvanized steel are also used in water sys tems and are subject to corrosion. The use of similar corrosion inhibitors is disclosed in U.S. Pat. No. 3,260,673 to Fisher, and No. 3,397,150 to Burt, et al., and No. 3,422,166 to Pitman.

l have found that the mono-, di-, and triphosphoric acid esters of triethanol amine and mixtures thereof are effective corrosion inhibitors without the necessity of adding zinc, chromates or other additives. These esters effectively inhibit the corrosion of metals in water systems when they are added in amounts of from about 10 to 100 mg/l either alone or in combination with from about 1 to 10 mg/l of an effective triazole or thiazole, as for example, mercaptobenzothiazole or benzotriaz ole.

The following table shows the results of experiments which demonstrate the effectiveness ofa mixture of the mono-, di, and triphosphoric acid ester of triethanol amine and the water-soluble salts thereof in inhibiting metallic corrosion. These tests were run in synthetic Pittsburgh water. Steel electrodes were used in polarization test cells with the initial pH at 7.0. Inhibitor concentrations were calculated on the basis of active material. The amount of corrosion that had taken place was determined from the current density at the intersection of an extrapolation of the so-called Tafel portion of the anodic polarization curve with the equilibrium or mixed potential value, usually referred to as the corrosion potential. E Application of Faraday's Lay allows a computation of a direct mathematical relationship between the current density of E,.,,,.,., expressed in amperes per square centimeter and a more useful corrosion rate expression such as milligrams of steel consumed per square decimeter of surface per day (m.d.d.) and mils per year (m.p.y.). This relationship is such that a current density value of 4.0 l0' amperes/cm 1.0 mg/dm /day. Further, the m.p.y. value is calculated from the usual formula: m.p.y. m.d.d. (1.44/density, using a density value of 7.87 g/cm for The following test provided corrosion rate data under field conditions. Pilot plant size cooling tower-heat exchanger test equipment (CTHE) was used to simulate large industrial recirculated cooling water systems. The makeup water for this experiment was a synthetically prepared tap water similar in analysis to Pittsburgh, Pennsylvania tap water. The pH of the water in the operating system was controlled to 7.0 t 0.1 by feeding a dilute solution of sulfuric acid on demand from an automatic pH control system. This simulation also included flow velocities of 2 5 ft./'sec., natural concentration of the minerals in the water to about five times their concentration in the makeup water (5X) by evaporation, several different metals exposed (but not galvanically coupled), three successive heat transfer surfaces, etc. This system is highly instrumented and prov vides substantial data relating to the performance of in hibitors since one can evaluate not only test coupons, but also steel and admiralty brass heat transfer surfaces, and continuously record instrumental corrosion rate data (Corrater instrument, Magna Corp., Santa Fe Springs, Calif). The aforenoted mixture of phosphate ester of triethanol amine was maintained at 30 60 mg/l during this test.

Corrosion rates on steel during this 3M2 week long test (the test ran continuously, 24 hrs/day, for twentyfour consecutive days) were 1.5 to 3.5 m.p.y. on test coupons; the recording Corrater chart showed a very stable value of 1.5 i 0.5 m.p.y. The heat transfer surfaces of the heat exchanger tubes were clean and essentially free of any corrosive attack.

The copper alloy specimens initially showed corrosion rates of 0.5 0.9 m.p.y. Since this is a bit high for copper alloys, 1 2 mg/l of a specific copper corrosion inhibitor, sodium mercaptobenzothiazole was fed to the system. This reduced the copper alloy corrosion rates to an acceptable rate of less than 0.1 m.p.y. Benzotriazole would be equally effective in this application. Both products are compatible with the ester and can be used interchangeably in a commercial preparation.

1 claim:

1. A method of inhibiting the corrosion of metals in a water system which comprise-s maintaining in the water of said system at least about 10 mg/l of a phosphoric acid ester of triethanol amine.

2. A method as in claim 1 which further comprises maintaining in said system at least about 1 mg/l of a member selected from the group consisting of thiazoles and triazoles.

3. A method as in claim 2 wherein the thiazole is mercaptobenzothiazole.

4. A method as in claim 2 wherein the triazole is ben- 

1. A METHOD OF INHIBITING THE CORROSION OF METALS IN A WATER SYSTEM WHICH COMPRISES MAINTAINING IN THE WATER OF SAID SYSTEM AT LEAST ABOUT 100 MG/L OF A PHOSPHORIC ACID ESTER OF TRIETHANOL AMINE.
 2. A method as in claim 1 which further comprises maintaining in said system at least about 1 mg/l of a member selected from the group consisting of thiazoles and triazoles.
 3. A method as in claim 2 wherein the thiazole is mercaptobenzothiazole.
 4. A method as in claim 2 wherein the triazole is benzotriazole. 